1. Field of the Invention
The present invention relates to a cutting device utilizing a pyrotechnic expansion tube for cutting at least one part, along a given cutting line.
Such a cutting device can more particularly be used in the aeronautical and space industries for the control, in a very short time of the separation of two structural elements, while ensuring the transmission of the sometimes high stresses and forces between the two elements, prior to cutting taking place.
2. Discussion of Background
Currently, when two metallic structures, having forces, stresses and loads passing therebetween, are to be irreversibly separated in a very short time and in a remotely controlled manner, pyrotechnic cutting devices integrated into the junction zone between the two structures, are often used.
When a clean cutting operation is desired to be carried out, so that with a minimum amount of dust is released, pyrotechnic expansion tubes are generally used.
The expression "pyrotechnic expansion tube" designates a tight, deformable metal tube, in which a detonating cord or fuse is passed therethrough. A flexible material, such as silicone rubber, is interposed between the detonating fuse and an envelope enveloping the detonating fuse. Prior to firing, the envelope has an oblong cross-section, e.g., in the form of an ellipse or flattened circle.
When the detonating fuse is fired, a shock wave, propagating at a very high velocity along the pyrotechnic expansion tube, deforms the envelope and tends to give the envelope a substantially circular cross-section.
Conventionally a pyrotechnic cutting device including a pyrotechnic expansion tube is used for cutting metallic parts. For this purpose, the pyrotechnic expansion tube is installed in a space between two metallic parts or between two portions of the same metallic part. The part or parts to be cut are previously machined, so as to have a reduced thickness zone along each desired cutting line. The expansion of the envelope, caused by the firing of the detonating fuse, leads to the cutting of the part or parts along the cutting line corresponding to the machined zone.
Devices for cutting one or two metallic parts by means of a pyrotechnic expansion tube are more particularly described in: U.S. Pat. No. 3,486,410; U.S. Pat. No. 3,453,960; U.S. Pat. No. 3,698,281; FR-A-2 598 796 and EP-A-0 273 061.
The structural elements used in the aeronautical and space industries are increasingly frequently made from non-metallic materials. In particular, the materials used are often composite materials, i.e., materials formed from long fibers arranged in the form of sheets superimposed in preferred orientations and embedded in a resin matrix.
When such non-metallic materials are used, it is not presently possible to directly cut the non-metallic materials with a pyrotechnic expansion tube, as is normally done with metallic structures.
Firstly, machining of a reduced thickness zone, in a non-metallic material and more particularly, in a composite material, the non-metallic material and/or the composite material being indispensable for localizing and limiting the cutting produced by the pyrotechnic expansion tube), is unacceptable. Thus, machining of a reduced thickness zone would most likely lead to unacceptably reducing the mechanical characteristics of the part to be cut prior to cutting by the pyrotechnic expansion tube, due to the long fibers of the composite material, giving the composite material its preferred characteristics, being cut.
Moreover, the cutting, of a non-metallic and particularly a composite material, may considerably pollute the environment, as well as significantly reduce the mechanical characteristics of the adjoining structures. This reduction in the mechanical characteristic of the adjoining structures can give rise to a de-lamination phenomena, i.e., a detachment of the fiber sheets in the vicinity of the cutting line.
Therefore, when a pyrotechnic cutting device presently has to be integrated into a non-metallic structure, a metallic structure is interposed between the two structural elements to be separated and the cutting of the two structural elements using a pyrotechnic expansion tube is controlled. In other words, separation is ensured by cutting one or more metallic parts joined to the assembly of two structural elements made from non-metallic material and which two structural elements to be separated. This conventional arrangement makes the cutting more complicated and increases costs.
The interposing of the metallic structure between the two non-metallic structural elements to be separated is contrary to one of the essential advantages brought about by non-metallic materials, i.e., savings in weight. Thus, the addition of metallic parts in the linking zone between the assembly of the two structural elements to be separated leads to a non-negligible weight increase. This weight increase is mainly due to the metallic character of the added parts and the need for fixing members to ensure the connection between the metallic parts and the non-metallic parts. This is a particularly prejudicial disadvantage in certain applications, such as in the space industry.
Moreover, the pyrotechnic cutting of metallic parts leads to the production of a relatively severe shock. This shock is applied to the often very sensitive instruments and equipment located in the vicinity. However, if direct cutting of the non-metallic material by a pyrotechnic expansion tube were possible, the very different mechanical characteristics of non-metallic materials would permit, separation while producing a much lower shock level. This would constitute an advantage for the possibly sensitive instruments and equipment located in the vicinity.